SAFETY VALVE, - 243 



III. 



(tefcriptlon of a Safety Valve, containing a Vacuum Valve in the 

 famt Hole of the Boiltr. By Sir A, N,Edelcrantz.* 



J N large boilers or coppers, where boiling fluids are en* Large boilers re- 



clofed, afufety valve is generally ufed to prevent their burft- ^alve and a va« 



ing, from an unexpedled exceffive force of the elaftic fleam, cuum valve. 



and, belides, a vacuum valve, to prevent their being com-^ 



prefled or craflied by the weight of external air, in the cafe 



of a fudden condenfation of the vapours. Thefe two valves 



are commonly fitted in two different holes in the boiler j but 



as a more fimple, and confequently more eligible, method 



feems to be that of joining them together, I take the liberty 



to fubmit to the Society for the Encouragement of Arts, &c, 



the following contrivance for that purpofe :— 



a b, Plate Jill. Fig. 2. is a common conical fafety valve, Defcriptlonofa 

 fixed in the boiler c d, having four openings, i i, which ^^^ f'frms both^*^'^" 

 reprefented in a plan view in Fig 3 : e / is the metallic rod, offices, 

 bearing the weight K K, with which the fafety valve is 

 loaded, and extending itfelf under that valve to/; g h is the 

 vacuum valve confiding in a plane circular plate, with a brafs 

 tube Hiding along the rod, and prefled by a fpiral fpring to 

 the fafety valve a b (againft which it has been well ground in 

 making it), clofing in that fituation the openings i i. 



Such being the conftrudion of the whole, it is evident, that It Is a loaded 



wheo the elafticity of the fleam increafes, the two valves, ^^^^^ opening 

 ... , . , . 1 , . . n 11 upwards J having 



jomed together, with the holes z i Inut, make but one, oppo- in its plate a 



fing to the elafticity of the fleam an united refiflance, which fp"ng -valve 



is regulated by the weight ^ ^, in the common way ; but, on wards, 



the contrary, when by condenfation of the vapours a vacuum 



is produced, the external air in preffing through i i, upon the 



vacuum valve g A, forces it down, and opens to itfelf a paffage 



into the boiler. 



The valve g h may eafily be made conical, like the other^ 



if that form fhould be preferred; but indifferent trials, thave 



found planes, if well turned and ground together, join as per- 



* From the Memoirs of the Society of Arts for 1804. The 

 filver medal was awarded for this Invention. 



R 2 feaiy 



